The invention relates to a belt retractor for a vehicular seat belt.
A conventional belt retractor comprises a belt reel rotatably mounted in a frame, two locking discs for blocking the belt reel, two energy absorbing elements, each of which is connected at one axial end to a locking disc and one of which is non-rotatably connected at an axial end to the belt reel, and two locking pawls capable of cooperating with the locking discs. Energy absorbing elements of a belt retractor serve to permit a controlled return rotation of the belt reel, i.e. in the unreeling direction of the webbing when the belt retractor is itself blocked, as soon as high forces act on the seat belt made available by the belt retractor. It is in this way that a force limiting function is achieved. The belt retractor provided with a force limiting function permits a controlled forward movement of the upper body of the vehicle occupant, achieved ultimately by plastic deformation of the energy absorbing elements.
Various concepts have already been proposed for influencing the webbing force from which the controlled return rotation of the belt reel in the unreeling direction of the webbing materializes. Depending on the severity of the collision and weight of the vehicle occupant to be restrained the intention is to achieve adaptation to the force with which the webbing is unreeled. One possibility of influencing the force of the webbing is to selectively activate/deactivate one of the energy absorbing elements, this also needing to be reliably assured in case the belt retractor is blocked.
The object of the invention is to further develop a belt retractor of the aforementioned kind to the effect that the force with which the webbing is unreeled can be reliably altered even during the belt reel being blocked.
According to the invention, a belt retractor for a vehicular seat belt comprises a belt reel rotatably mounted in a frame, two locking discs for blocking the belt reel and two energy absorbing elements. The energy absorbing elements are each connected at an axial end to a locking disc and one of which is non-rotatably connected at an axial end to the belt reel. The belt retractor further comprises two locking pawls that are capable of cooperating with the locking discs. At least one of the locking pawls is releasably connected in a starting position to the frame by a connecting element. Making use of such belt retractor now makes it possible, for example, where a heavy vehicle occupant or a severe collision is concerned, to make use of an energy absorbing element having a high torsional resistance. If adaptation is needed, for example, during a lighter-weight vehicle occupant being jolted forwards or in the case of a less severe collision, then the connecting element can be moved by an unlocking element into an end position, so that the locking pawl is released from the frame, and locking pawl and frame are no longer connected to each other. This results in a second energy absorbing element being made use of to reduce the torsional resistance so that it results in lighter restraining forces acting on the vehicle occupant.
It is preferably provided for that the unlocking element can be acted upon by an actuating element. The unlocking element is a simple mechanical component capable of reliably acting on the connecting element when the unlocking element is acted upon by the actuating element. Hence, this makes it possible by particularly simple and rugged means to release the locking pawl from the frame and, with this, to make use of the second energy absorbing element such that a reduced belt unreeling force is produced.
In a further advantageous embodiment it is provided for that the connecting element comprises a mounting hole in which an axle is mounted, and the locking pawl comprises an aperture by which it is pivotally mounted on the axle. When the connecting element is urged from its original position by action of the unlocking element, the locking pawl is able to leave its locating position on the axle. When the aperture in the locking pawl has substantially the shape of an elongated hole and comprises a constriction, the axle is able to overcome the constriction as of a defined force and the locking pawl is released. This can be achieved also by the aperture in the locking pawl being covered in a partial area by a thin wall element. As of a defined force, the axle is able to break open the wall element and the locking pawl can leave its locating position on the axle.
Advantageous aspects of the invention will be apparent from the subclaims.